High-temperature electric resistance oven



2 SHEETS-SHEET 1 Filed June 3, 1947 M w s96; fidends S. KLEIN HIGH-TEMPERATURE ELECTRIC RESISTANCE OVEN Feb.l2, 1952 2 SHEETSSHEET 2 Filed June 3, 1947 Fig,

[m enzar \ZEGFRIA'O A251 Patented Feb. 12, 1952 UNITED STATES PATENT OFFICE HIGH-TEMPERATURE ELECTRIC RESISTANCE OVEN Application June 3, 1947, Serial No. 752,023 In France June '7, 1946 6 Claims. 1

With a view to obtaining high temperatures in electric resistance ovens, for want of electric leads having a melting point higher than the temperature to be attained, it has already been proposed to use metals in the liquid state, yet a satisfactory industrial efiiciency has never been obtained in this manner.

Such lack of useful efficiency is due mainly to the fact that the metals have been employed in the open air, or at all events with an insufficient protection against oxidation, which leads to disaggregation by chemical transformation.

It has also been proposed to use the metals in the form of coils embedded in refractory materials intended to maintain them when they are in the liquid state, but the results obtained have again been disappointing, probably due to the fact that refractory materials pervious to the air were employed and a rapid oxidation of the molten metal took place.

This invention has for its object a high-temperature electric resistance oven in which threadlike metallic electric resistances in the liquid state are used which are maintained in a sheath of high-melting refractory material by which they are kept in the desired form, e. g. that of a coil, characterized thereby that said sheath is constituted by a tube of refractory material impervious to the air.

Thus, excellent results have been obtained by against breakage and deformation by a covering 3* of high-melting refractory material such as aluminum oxide or powdered silica. The whole is surrounded with a mass of high-melting refractory material which likewise may be alu minum oxide or silica powder. Ihe deformations to which those parts of this assembly which have unequal coefficients of expansion are subjected by heat are liable to cause breakages notably as the conducive metal melts. In order to remove this danger care is taken to preparatorily heat up the aggregate with the aid of an additional e. g. nickel-chromium resistance and to send the main current through the conductive metal only after same has melted.

According to a further characteristic of the invention the heating is performed with the aid of high-frequency currents; in this manner, the heating by convection and conduction is supplemented with a heating by induction; a tin electrode is particularly advantageous for that 2 purpose owing to the low ohmic resistance opposed therehy to alternating currents.

The crucible proper may be made of graphite, in which case high-intensity currents are induced thereby by which the heating eiiect is increased.

According to another characteristic of the invention, in order to exclude any possibility of oX- idation of the conductive metal at the ends of the duct containing the same, said duct may be evacuated.

A further characteristic of the invention consists in providing means adapted as desired to create a flow of molten metal, particularly of molten tin, through the quartz tube, whereby bubbles that may have formed and which interfere with the flow of electric current can be flushed up to the ends of said quartz tube.

For that purpose, there may be provided a cupule at either end of the quartz tube and an additional cupule communicating with the middle portion of aforementioned tube through a complementary section of said tube, and means, which may be pneumatic, to force out the molten metal present in the last-mentioned cupule to replace the metal distributed in said tube, which is forced into the other two of said cupules, thus carrying away the bubbles that may be present in it.

Another characteristic of the invention consists in arranging the cupules at a level sufficiently high to create a hydrostatic pressure which precludes the formation of metal vapours before the metal reaches its vaporization temperature.

The invention will be understood more completely by the reading of the following description, reference bein bad to the appended diagrams in which:

Figure 1 is a diagrammatical view taken on a vertical section of the oven.

Figure 2 is a front view of the oven resistance according to another embodiment of the invention.

Figure 3 is a plan view.

The tin I or some other similar conductive material that melts at low temperature and volatilizes at a very high temperature is used as the lead; it is contained in a quartz tube 2. Said quartz tube 2 has the shape of a coil or cylindrical spiral. It opens at either end thereof in funnel-like flaring portions 3 arranged at the same level and which prevent the tin from overflowing as the same expands upon heating. The quartz tube as a whole is embedded in an annular layer 2 of silica powder.

An additional covering 5 of silica powder surrounds the whole.

The electrodes 6 are located in the funnels 3 in contact with the tin l.

A nickel-chromium lead I surrounds the oven and the cupules for the preparatory heating up of the whole before the current is sent through the main resistance.

In the embodiment illustrated in Figs. 2 and 3 the resistance is constituted by a quartz tubular coil 2| filled with tin 22, the crucible (not shown) being arranged coaxially therewith. The ends of the coil are connected with each other by tubular sections 23, likewise made of quartz, of sufiicient height, leading to cupules 24 which may or not be fixed and whose capacity is at least equal to that of the tube 2|. The current lead-in electrodes 25 dip into said cupules which normally are halffilled with metal. The metal may be covered with a protective layer.

Connected with the middle portion of the quartz coil is an additional quartz tube section 26 leading from a third cupule 21 and located on a level with the cupules 24.

Pneumatic means 28 enable to suddenl force out all the molten metal present in the whole coil 2|, which then fills the two cupules 24. the bubbles that may have formed in the metal are thus driven away and escape from said cupules 24; it is only necessary to release the air or like pressure acting upon the metal contained in the cupule 21 to allow the metal to assume its original position, the tube then being filled with bubbleless metal and each cupule 24 and 21 being half-filled.

Only two cupules, or more than three cupules, might be provided without departing from the scope of the invention.

What I claim as my invention and desire to secure by Letters Patent is:

1. An electric heating resistance for the obtainment of very high temperatures comprising a tube made of fused silica extending upwards in a cupule, a low melting, high volatilizing metal filling said tube completely and said cupule partly, electrodes to lead current to said metal dipping in said metal the level of metal in the cupule being such that a hydrostatic pressure is created within said tube by which the formation of metal vapor bubbles within the tube at workin temperature is precluded.

2. An electric heating resistance according to claim 1 wherein each upwardly projecting end of the tube extends in a cupule, the said cupules being filled with a metal up to such a level that a hydrostatic pressure is created within the tube by which the formation of metal vapor bubbles within the tube at working temperature is preeluded.

3. An electric oven for the obtainment of very high temperatures comprising at least one electric heating resistance consisting of a tube made of a refractory material, an extension of said tube projecting upwards out of the oven, a metal filling the tube completely in its enclosed portion and partly in its upwardly projecting ex- All tension, the level of metal in the latter being such that a hydrostatic pressure is created within said tube by which the formation of metal vapor bubbles within the tube at working temperature is precluded.

4. An electric heating resistance for the attainment of very high temperatures comprising a tube made of a refractory material composed of fused quartz, having a portion substantially coextensive with the heating resistance and a portion extending a substantial distance upward therefrom and terminating in a plurality of cupules, a low-melting, high volatilizing metal filling said tube completely and said cupules partly, electrodes to lead current to said metal within said cupules, the hydrostatic pressure head due to the filling of said extensions and cupules preventing the formation of metal and vapor bubbles within the tube at working temperature.

5. An electric heating resistance for the obtainment of very high temperatures comprising a tube made of a refractory material, having a portion substantially co-extensive with the heating resistance and a portion extending a substantial distance upward therefrom and terminating in a pluralit of cupules, a low-melting high volatilizing metal filling said tube completely and said cupules partly, electrodes to lead current to said metal within said cupules, an additional member connected at one end to the refractory tube and at the other end to pneumatic means.

6. An electric oven for the obtainment of very high temperatures comprising at least one electric heating resistance according to claim. 5 and including an electric resistance to preheat the oven before the first mentioned resistance is switched in.

SIEGFRIED KLEIN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 821,418 De Kando May 22, 1906 1,078,619 Greene Nov. 18, 1913 1,350,714 Foley .1 Aug. 24, 1920 1,402,332 Brown Jan. 10, 1922 1,551,766 Northrup Sept. 1, 1925 1,568,848 Kellendorfer Jan. 5, 1926 1,637,167 Weckerle July 26, 1927 1,878,392 George Sept. 20, 1932 1,979,609 Ferguson Nov. 6, 1934 2,101,675 Ferguson Dec. 7, 1937 2,121,141 De Lange June 21, 1938 2,253,981 Peyches Aug. 26, 194 2,397,445 Stupakoff Mar. 26, 1946 OTHER REFERENCES Strong: Procedures in Experimental Physics (Prentice-Hall Inc. New York, New York, 1946) chapter V. 

